Decoding circuit



April 21, 1953 B. H. SINCLAIR DECODING CIRCUIT Filed March 4, 1952 RECEIVER BIAS FIG. I

FIG. 2

INVENTOR.

BERT H.SINCLA|R Patented Apr. 21, 1953 DECODING CIRCUIT Bert H. Sinclair, Little Silver, N. J., assignor to the United States of America as represented by the Secretary of the Army Application March 4, 1952, Serial No. 274,818

6 Claims. (Cl. 340-467) (Granted under Title 35, U. S. Code (1952),

sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

This invention relates to a decoder for use with pulsed wave signals. In particular it relates to a decoder adapted to receive paired pulse signals and adjustable to produce an output signal only in response to signals having a particular time spacing between the pulses of a pair. It further relates to a flexible decoder for receiving pulse signals and which may be set to respond to paired pulse signals only, or to single pulse signals.

A number of circuits have been devised for responding to paired pulse signals and to multiple pulse signal groups having particular pulse spacings, so that only particular coded groups of pulses will produce an output signal from the decoder. These circuits, in general, are expensive to build and precise in operation and systems employing such arrangements are frequently found to be of limited use because of the precision requirements. These prior art arrangements generally employ relatively expensive delay lines which predetermine the decoding operations. The tolerance imposed by the use of such delay lines is very narrow and for some purposes these over-precise arrangements defeat their own purpose.

For certain electronic applications it is desirable to provide an arrangement which responds to a coded signal of spaced pulses, but which is fairly tolerant of the time spacing of the pulses and one which may readily be adjusted to accept coded pulses with different time spacings. For such type of service the precision circuits of the prior art have no value.

Accordingly, it is an object of the present invention to provide a decoder circuit for use with paired pulse signals which is adjustable to respond to pulses of a pair having substantially a particular time spacing and which may be readjusted readily to accept paired pulse signals with a different time spacing. object of the present invention to provide a decoder for receiving pulse signals which may be set to operate in one mode to respond to paired pulse signals, but which may readily be changed to accept and operate with single pulse signals.

In accordance with the present invention there is provided a decoder for paired pulse signals which is adjustable to respond to pulses of a pair having substantially a particular time spacing. The decoder is comprised of a condenser and resistance time constant circuit and a source of operating voltage. Means are provided for utiliz- V It is a further 7 ing the source to provide limits of charge and discharge for the condenser and means to adjust at least one of the limits. Also provided are means responsive to a first received pulse signal for rapidly charging the condenser to one limit and means comprising a resistor for exponentially discharging the condenser to the other limit to provide a condition of operation such that the occurrence of a second received pulse signal during a limited time interval following the charging rapidly completes the discharging and means re sponsive to the rapid discharging for producing an output signal.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a circuit diagram illustrating a preferred embodiment of the decoder and Fig. 2 is a series of graphs for use in explaining the operation of the system.

Referring to Fig. 1 of the drawing, a radio receiver H, having a receiving antenna [0, is employed to receive pulse modulated carrier wave signals and to amplify and rectify these pulses and supply them to the input windin of transformer I2. The transformer l2 operates to differentiate the output pulse signals from receiver I I and supply them to the control grid of vacuum tube IS. The output of tube 13 is coupled to the input of vacuum tube M. The tube I4 is provided with'conventional plate and cathode load impedances, so that its output can be coupled to the input of the triode vacuum tube ll via the switch l5 and condenser It in either of two polarities. A

suitable input impedance and operating potential for the grid of tube IT is provided by means of the resistance network shown, which includes the resistor 25 and potentiometer 18. The position of the potentiometer I3 is normally set to provide a slight positive bias to the grid of tube H. The

output of tube I1 is coupled to the input of tube 19. Tube 1 9 is provided with a negative grid bias and is organized to operate as a cathode follower circuit by virtue of the inductance 20 and resistance 2| connected in series in the cathode circuit. The cathode output circuit is connected by the network consisting of condenser 22, rectifier 23 and condenser 24 to the output terminals.

Considering now the operation of the system,

pulse modulated carrier wave signals are received by antenna [0 and supplied to the input of re ceiver II, where they are amplified at radio irequency, rectified, further amplified at video frequency and supplied to the input of transformer 12 as pulse video signals. The secondary winding of transformer l2 operates to difierentiate received pulsesignals and is of such polarity that difierentiated pulse signal produced between the control grid and cathode of tube [3 is comprised of a narrow positive pulse corresponding to the trailing edge. The choice of circuit constants and operating potentials are such that grid current is drawn on the occurrence of. the positive pulse and therefore only the narrow negative pulse is reproduced by tube [3. the differentiation is to convert received pulses of any width to narrow pulses of uniform width. The output from tube #3 is, accordingly, in the form of narrow positive pulses of uniformamplitude as applied to the grid of tube [4. As indi, cated in the drawing, the-output from the plate circuit of tube ill consists of pulses of, negativepolarity and that from the cathode circuit of tube ldcon'sists of pulses of positive polarity. With switch iii in the down, position as shoum, pulses of positive polarity are coupledviacondenser IS- to the grid oftube ii;

The decoder proper is the portion of the circuit comprising tubes ll'and l9 and, the operation is,

illustrated by the Fig. 2 graphs. In columnA,

graph I, two positive pulses of a-v paired pulse signal are shown as they would appear for application to the'grid, of tube IT; The grid of tube.

l1, as-heretofore' stated, is at av slightly positive potential relative to its cathode by virtue of the setting of potentiometer ldand, accordingly, the condenser iii has a fixedvalue of charge which is determined bythis setting since it will be clear that some grid current flows in, tube il in the normal condition of the circuit. When the first, positive pulsersignal is applied to the grid of ii, more grid current is drawn rapidly to charge condenser it to a negative value which is one limit of charge as shown in graph 2' of column A. Thereafter, condenser It starts to discharge exponentially as shown in the graph.

The form and magnitude of the exponential discharge curve is determined by the capacity value of condenser it and the resistances in series with it (principally resistor 25) which form the time constant circuit and alsov the limits of charge and discharge. Theselimitsare set by the amount of' grid currentdrawnwhen the first pulse occurs and the final value of dischargepotential,set, by potentiometer l8;

Theoccurrenceofthesecond pulse of'the pair, which is shown to occur duringthe exponential discharge period, operates to complete the discharge to the limit set by-potentiometer l8, and to accomplish this completion very'rapidly. Accordingly, the plate voltage of, tube I! has the form hown in graph 3. This wave', as coupled to the grid of tube i9, is of the form shown in graph 4 where it is shown related to, the dotted line representing the grid cut-01f bias. This bias ischosensothat only the upper part of graph 4 is effective as a single wide pulse. Normally this wide pulse voltage would be repeatedin the same polarity across the cathode output impedance of tube lilbut, as previously stated, this cathode load.

circuit is comprised of inductance 2i], and resistor 2| to operate as a differentiating circuit. Accord,- ingly, the voltage developed across'the cathode output. of tube. is is differentiated andhas the double pulse form shOWn in graph 50f column A. This form consists of an initial positive pulse and a. following negative pulse. The rectifier 23 is The purpose of suitably biased as indicated in the drawing and, accordingly, only a negative output pulse, as shown in graph 6 of column A, is produced. It is evident, therefore, that the application of a pair of, positive pulses applied to the grid of tube ll, that is, to the input of the decoder, operates to produce a single negative output pulse for the conditions above described.

The rejection by the decoder circuit of a single negative pulse signal applied to the grid of tube H is illustrated in column B, where it is shown (graph I) that a single positive input pulse signal causes grid current to be drawn in tube I! and so producesan output wave of the form shown by graph 2. Condenser I6, as the wave form shows, is rapidly charged and then, in the absence of a second received pulse, continues a complete exponential discharge. The remaining graphs 3, 4, 5, and 6 of column 3 illustrate that when this exponential discharge is not interrupted and rapidly completed by the reception ofa second pulse, then the differentiation in the cathodecircuitof tube is produces only a single positive pulse and no negative pulse and, accordingly, there is no output from the decoder.

Comparing now columns A and B of Fig. 2, it is evident that, with the-setting of potentiometer [8 for the conditions of operation thus far described, if the second pulse of the pair occurred after the exponential discharge were completed its eifect would be to once more causegrid current to be drawnin tube l7 and would not accomplish any rapid completion of condenser discharge such as would produce an output pulse-from the decoder.

Thus, for a given setting of potentiometer i8, pulses of apair which are time spaced too wide will produce no response. Similarly, if the second pulse of a pair occurs too quickly following the first pulse, as for example when the condenser 16 is still being charged, then again therecan be nov operation to produce an output signalfrom the decoder. Accordingly, the setting of potentiometer l8 will determine, a condition of operation for response to time space pulses Whenthe second pulse of the pair occursat a suitable time afterthe first pulse.

In dotted line the response of the decoder is indicated for more widely spaced pulsesin graphs and 2 of: column A and it will be evident from thedescription thus far given that this response to wider spaced pulses may be accomplished by changing one of the limits of charge by suitable adjustment of potentiometer [8.

Accordingly, it will be clearthatitheidecoder is. one, having fairly wide tolerances to the spacingv widely spaced pulses is not desirablasince. noise or an interfering; pulse occurring in; the space interval would interfere with, the: operation.v In practice, paired pulse signals having a timespacing of a. few. microsecondshave-been, efliciently' employed with the described decoder, circuit.

For some types of operation itisdesirablexto: have the decoder respond to single pulselsi'gnala. Inthe arrangement or the present; invention, -this;.

is accomplished by. simply throwing switch. [S to the up position, whereby; received; pulses; are. applied to. the grid of tube If! in negative: polarity.

The operation is illustrated by the graphs Hi 01" column C, Fig. 2. It will be evident from these graphs that when negative pulses are so applied there is no additional grid current drawn in tube ll, rapidly to charge the condenser it, but instead there is merely a repeating oi the applied pulse which, when differentiated by circuit elements 2!] and 24, results in a negative pulse output. Accordingly, the decoder wili respond to single pulse signals with switch [5 in the up position and will respond to paired pulse signals of a particular time spacing when the switch is in the down position.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

What is claimed is:

l. A decoder for paired pulse signals, which is adjustable to respond to pulses of a pair having substantially a particular time spacing, comprising a condenser and resistance time constant circuit and a source of operating voltage, means utilizing said source to provide limits of charge and discharge for said condenser and means to adjust at least one said limit, means responsive to a first received pulse signal for rapidly charging said condenser to one limit, means comprising said resistor for exponentially discharging said condenser to the other limit, to provide a condition of operation such that the occurrence of a second received pulse signal during a limited time interval following said charging rapidly completes said discharging, and means responsive to the rapid discharging for producing an output signal.

2. A decoder for paired pulse signals which is adjustable to respond to pulses of a pair having substantially a particular time spacing comprising a condenser and resistance time constant circuit and a source of operating voltage, means utilizin said source to provide limits of charge and discharge for said condenser and means to adjust at least one said limit, means responsive to a first received pulse signal for rapidly charging said condenser to one limit, means comprising said resistor for exponentially discharging said condenser to the other limit, to provide a condition of operation such that the occurrence of a second received pulse signal during the time that said discharge approaches said other limit rapidly completes said discharging, and means responsive to the rapid completion of said discharging for producing an output signal.

3. A decoder for paired pulse signals which is adjustable to respond to pulses of a pair having substantially a particular time spacing comprising a condenser and resistance time constant circult and a source of operating voltage, means utilizing said source to provide limits of charge and discharge for said condenser and means to adjust at least one said limit, means responsive to a first received pulse signal for rapidly charging said condenser to one limit, means comprising said resistor for exponentially discharging said condenser to the other limit, to provide a condition of operation such that the occurrence of a second received pulse signal during a limited time interval following said discharging rapidly completes said discharging and means comprising a differentiating circuit responsive to the rapid discharging for producing an output pulse signal.

4. A decoder for paired pulse signals which is adjustable to respond to pulses of a pair having substantially a particular time spacing compris ing a condenser and resistance time constant circuit and a source of operating voltage, means utilizing said source to provide limits of charge and discharge for said condenser and means to adjust at least one said limit, means responsive to a first received pulse signal for rapidly charging said condenser to one limit, means comprising said resistcr for exponentially discharging said condenser to the other limit, to provide a condition of operation such that the occurrence of a second received pulse signal during a limited time interval following said discharging rapidly completes said discharging, limiting means for converting said discharging to a pulse Wave having steep leading and trailing edges and means responsive to said trailing edge for producing an output pulse signal.

5. A decoder for paired pulse signals which is adjustable to respond to pulses of a pair having substantially a particular time spacing comprising a condenser and resistance time constant circuit and a source of operating voltage, means utilizing said source to provide limits of charge and discharge for said condenser, a vacuum tube having anode, cathode and grid control elements, means comprising the grid-cathode path of said tube for rapidly charging said condenser to one limit, means comprising said resistor for exponentially discharging said condenser to the other limit to provide a condition of operation such that the occurrence of a second received pulse signal during a limited time interval following said discharging rapidly completes said discharging, means responsive to the rapid discharging for producing an output signal and means to adjust said other limit to cause response for a different time spacing.

6. A decoder for pulse signals having one mode of operation in which it is adjustable to respond only to pulses of a pair having substantially a particular time spacing comprising a condenser and resistance time constant circuit and a source of operating voltage, means utilizing said source to provide limits of charge and discharge for said condenser and means to adjust at least one said limit, means for applying received pulse signals in one polarity to said decoder, means responsive to a first received. pulse signal for rapidly charging said condenser to one limit, means comprising said resistor for exponentially discharging said condenser to the other limit, to provide a condition of operation such that the occurrence of a second received pulse signal during a limited time interval following said charging rapidly completes said discharging and means responsive to the rapid discharging for DIOdLlClZlg an output signal and means for providing a second mode of operation responsive to single pulse signals comprising means for applying received pulse signals in the opposite polarity to said decoder.

BERT I-I. SINCLAIR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,275,930 Torcheux Mar. 10, 1942 2,399,668 Francis May 7, 1946 2,484,352 Miller Oct. 11, 1949 

